Field
The present disclosure relates generally to energy storage devices, and more particularly to metal and metal-ion battery technology and the like.
Background
Owing in part to their relatively high energy densities, light weight, and potential for long lifetimes, advanced metal and metal-ion batteries such as lithium-ion (Li-ion) batteries are desirable for a wide range of consumer electronics. In many applications, Li-ion batteries have essentially replaced nickel-cadmium and nickel-metal-hydride batteries. Despite their increasing commercial prevalence, however, further development of metal-ion batteries is needed, particularly for potential applications in low- or zero-emission hybrid-electrical or fully-electrical vehicles, consumer electronics, energy-efficient cargo ships and locomotives, aerospace devices, and power grids. Such high-power applications will require electrodes with higher specific capacities than those used in currently-existing Li-ion batteries.
One of the areas in need of further development is the battery electrolyte. Several types of electrolytes can be used in batteries at moderate temperatures (e.g., below about 120° C.), including liquid organic electrolytes, ionic liquids, organic-polymer solid electrolytes, inorganic solid electrolytes, and mixed electrolytes. Common examples of inorganic solid electrolytes for Li-ion batteries include sulfide-based electrolytes (such as Li2S—P2S5, Li2S—Ga2S3—GeS2, Li2S—SiS2, etc.), oxide-based electrolytes (such as Li—La—Ti—O garnet, Li—La—Ta—O garnet, Li—Si—O glass, Li—Ge—O glass, Li9SiAlO8, etc.), mixed sulfide-oxide electrolytes (such as Li2S—SiS2—Li4SiO4, LiI—La2O2S—La2O2S2, etc.) and others. There are several advantages to using inorganic solid electrolytes in batteries operating at moderate temperatures, including their broad operational temperature windows, relative safety, reduced irreversible capacity losses, higher operational voltage windows, longer cycle life, and production compatibility.
Nevertheless, the use of inorganic solid electrolytes in particular has proven difficult to implement in practice and conventional commercial batteries operating at moderate or room temperatures almost never use inorganic solid electrolytes. This is because the conventional procedures for the formation of electrodes with inorganic solid electrolytes are not very efficient and suffer from several limitations, which reduce the current effectiveness and practicality of inorganic solid electrolytes.
These conventional procedures used to form electrodes with inorganic solid electrolytes typically involve the following lengthy (and often expensive and/or time-consuming) steps: (i) thorough mixing (or milling) powders of active material with conductive carbon powder and with solid electrolyte particles to form a homogeneous mass; (ii) casting the resultant mass on a flat substrate (such as a metal current collector foil); and (iii) annealing at elevated temperatures (and typically under pressure) in an inert environment to cause sintering of all the particles and the formation of an ionically conductive composite with electrically connected active particles. However, in order for the active particles to be electrically connected, high amounts of conductive carbon additive powder is used (sometimes as high as 30% or more). Since such powder (if in the cathode) does not typically participate in energy (ion) storage, the high amount of carbon powder reduces the specific (per unit mass) and volumetric (per unit volume) capacities of the electrode. In comparison, battery electrodes produced for use with liquid electrolytes commonly contain as little as 2-5% conductive carbon additives.
Similarly, in order to ensure that all active particles are ionically connected in the sintered composite via the solid electrolyte, the amount of solid electrolyte is often increased substantially (sometimes as high as 50% by volume or more). In comparison, commercial battery electrodes are typically infiltrated with as little as 25% by volume of the electrolyte or even less. This also contributes to the lowering of the specific and volumetric capacities of the battery. In addition, in many cases the interface between the solid electrolyte and the active particles contains excessive voids, which undesirably increases the polarization resistance and thus lowers the power performance of the battery (while also increasing the charging and discharging times).
Still further, the mixing and sintering of many metal-ion containing active anode particles (such as lithiated graphite or lithiated silicon for use in combination with Li-free cathodes in Li-ion batteries) must be performed in an inert (air-free) environment due to the high reactivity of such particles with air. The electrode fabrication equipment line (especially the one that includes mixing, casting, and annealing/sintering steps) occupies a large area. Sealing such equipment from air therefore becomes very expensive, which significantly increases the electrode production cost. In addition, if voids remain in the electrode after sintering, they may provide paths for air to reach and react with the metal-ion containing active particles.
Accordingly, despite the advancements made in electrode materials, high capacity metal-ion batteries remain somewhat limited in their application and there remains a need for improved batteries, components, and other related materials and manufacturing processes.